A technique devised for precracking single-edge notch beam KIc specimens of cemented carbides has been extended to several nonmetallic materials. The mechanism of formation and growth of a precrack under an indenter is discussed in terms of indentation theory, the material and geometry of the indenter, and the properties of the specimen material. For cemented carbides, the material's fracture toughness and the indenter angle appear to be the most important parameters governing the stability of a precrack, and this is probably true for other materials.

In materials with very fine or poorly defined precracks, it has been shown that a compliance method can be combined with the wedge indentation precracking procedure to enable KIc to be determined without measuring the crack length.